Cathode ray tube screen



Patented Nov. 21, 1939 CATHODE RAY TUBE SCREEN Max Knoll, BernhardBartels, and Otto Spengler,

Berlin, Germany, assignors to Telefunken Ge- .sellschaftfiir DrahtloseTelegraphic m. b. H.,

' Berlin, Germany, a corporation of Germany Application April 19, 1937,Serial No. 1375993 2 In Germany March 19', 1936 g 1 4. Claims.

This invention relates to electric signalling, and in particular, tofacsimile and television transmission systems utilizing cathode rayscanning means. i

This invention is an improvement upon the method and means. for electricsignalling disclosed in my co-pending application Serial No; 106,301,filed October 19, 1936 by Fritz Schroter and Max Knoll, and entitledTransmitter systern, and now Patent Number 2,156,435.

' In certain types-of transmission, it is desirable to scan astill'picture or sign either for testing advertising or identificationpurposes. For example, in a television transmitting station, it isdesirable at the end ,of a program to identify the station transmittingthe television program.

This identification might comprise the call letters of the station andinclude some symbol used as a trademark or identification sign by thestation. Such a symbol or picture, aswell as the call letters, may wellbe a half-tone picture. Instead of using the studio scanner for scanningthe picturesurface for this short in accordance with the inventiondisclosed in the above identified application, this invention teachesthe use of a special scanner which makes use of the different secondaryemission properties of two or more materials. According to the' presentinvention, a supporting surface -for'the picture to be transmitted ismadeof one' material, while the picture proper is made cfanothermaterial and supported on the surface of the plate. A cathode ray scansthe picture area and depending uponwhether the ray impinges on anelemental area of the support, orupon an elemental area of the pictureproper, more or less secondary'electrons will be released in accordancewith the secondary emission properties, which I characterizes thesupporting surface or the elements of the picture proper. An electrodeserves to capture the released secondary electrons and these electronsserve in turn to produce a voltage (Cl. ZED- 150) in which Fig.1 showsschematically a cathode ray-scanning system for use with the plateprepared in I accordance with our invention, and

Fig. 2 shows a cross-section of a half-tone plate'prepared according toour invention.

Referring now to the drawing, in Fig. 1 a cathode ray tube is showncomprisingv a glass bulb designed partially as and with the shape of acylinder, attached to which is a frustrum of a cone. Within thecylindrical portion of the reading the description together with theclaims, t

glass bulb a cathode ll andelectrode 22 are shown conventionallyconnected with a battery 23 to provide an'electron gun for concentratingand accelerating the electrons to provide a beam of high speedelectrons.Two pairs of deflecting plates l2 and I3 are arranged at right angles toeach other for purposes of deflecting the beam of electrons generatedwithin the electron gun so that the beamtraverses a predeterminedpattern of scanning. These electrodes may, for example, be supported bythe wall structure of the tube It or as is more usual, be supported'fromthe gun structure as is well known in the prior art. frustrum portion ofthe tube I ll intermediate the deflecting plates l3 and the half-toneplate I5. Connected between the plate l5 and the electrode 14 is abattery 16 in series with aresistance l1 to which are connected theterminals I8. The cathode ray beam scanning the plate I 5 causessecondary electrons to be ejected there- A metal electrode I4 'ispositioned in the from due to the velocity of impact upon the plate Iand these secondary electrons are collected by the electrode [4 andcurrent flow in accordance with the electrons reflected through theresistance ll, which gives rise to signal voltage for transmitting theelectro-optical effects.

Fig. 2 shows in cross sectional view, the plate 15. The plate l5may bemade of metal, such as aluminum, for example, upon which the halftoneimage is arranged in accordance with the half-tone screening methods andfurther, .differs in this respect from the invention disclosed in theabove identified copending application of Schroter and Knoll, in thatthe co-pending application provides a plate which is photo-elec-. 1trically engraved or recessed, the recesses being filled with carbon orsome other material having a different secondary emission characteristithan the supporting plate l5. 1

As will be appreciated, photo-engravingproc esses require considerablecare to be taken, and are, relatively speaking, a complicated process.

. tone screening details.

Applicants, therefore, have done away with the necessity of using aphotographically etched plate by providing a plate upon which thepicture proper is disposed upon the supporting metal plate. In general,the process consists in coating the smooth surface of the plate with aphoto-chemical substance. By photo-chemical substance is meant asubstance Whose chemical and physical properties undergo changes whenexposed to light. And for this purpose, applicants may utilize a coatingof chrome gelatin, which comprises gelatin in which has been includedpotassium bi-chromate. Such a gelatin is soft and pliable, but uponexposure to light, the area of the chrome gelatin so exposed, hardens.Thereafter, if the layer is Washed in water, the unexposed portions arewashed away, leaving in relief the portions of the film which have beenexposed to light which are insoluble. The changed chrome gelatinremaining upon the layer has secondary emission properties which are notgreatly different from carbon, and consequently, differs appreciablyfrom the secondary emission properties of the metallic plate supportingthe film of chrome gelatin. Thus, to prepare the plate, it is merelynecessary to flow the chrome gelatin upon the polished surface of theplate in the dark, exposing the plate to the picture of whichrepresentation is desired, by projecting the picture upon the plate andthrough a halftone screen where the picture is different from a blackand white picture, to provide the half- Thereafter, the plate is rinsedin water and the unexposed portions of the gelatin layer are washedaway, leaving the raised portions I9 upon the plate I5. The plate I5 isthen dried and may then be sealed in the tube for generating the signalsabove described.

Alternatively, a solution of bitumin of judea dissolved in oil orlavender may be flowed across the plate to provide the photo-chemicalvariable layer. The action of light makes the bitumin insoluble so thatafter exposing the picture through a half-tonescreen upon the layer ofbitumin on the metal plate, the plate maybe developed in oil oflavender, which removes the unexposed bitumin. The plate is then driedand may be used, as indicated above, for the chrome gelatin plate abovedescribed.

It will be appreciated, of course that the metal plate may be of someother metal other than aluminum, such as copper or nickel or tantalum,or any other metal whose secondary emission properties are differentthan the properties of the picture elements in relief upon the plate.

It will thus be appreciated that applicants new plate provides a simplerplate for use in a cathode ray scanner and that the combination ofapplicants plate and the cathode ray scanner described above results inan improved method of transmitting the electro-optical representations.

Having described our invention, what We claim is:

1. A cathode ray tube comprising an envelope, means for producing afocused beam of electrons within the envelope, means for deflecting theproduced focused beam of electrons in two mutually perpendiculardirections, a planar electrode of predetermined specific secondaryelectron emissivity, isolated minute particles of a material having aspecific secondary electron emissivity different from that of theelectrode positioned on the electrode and forming a halftone picture,the area .of said particles corresponding to the density of theelemental areas of the half-tone picture, said electrode beingpositioned to be impacted by the deflected beam of electrons, and meansto collect secondary electrons emitted from the particles. and theelectrode under the impact of the deflected focused beam, said beamproducing means, said secondary electron collecting means and saidelectrode being within said envelope.

2. In combination, means for producing a focused beam of electrons, atarget electrode of predetermined specific secondary electronemissivity, a plurality of elemental particles of a material having adifierent specific secondary electron emissivity than that of theelectrode, said particles being positioned on the target electrode toform elemental areas of a-half-tone picture, the area of said particlescorresponding to the density of the elemental areas of the half-tonepicture, means for deflecting the focused beam to scan substantially theentire area of the target and all of the plurality of particles to causesecondary electrons to be emitted from the target and plurality ofparticlesand means to collect the emitted secondary electrons, beamproducing means, said secondary electron collecting said means and saidelectrode being Within said envelope.

3. A cathode ray tube. comprising an envelope, means for producing afocused beam of electrons within the envelope, means for deflecting theproduced focused beam of electrons in two mutually perpendiculardirections, a planar metallic electrode of predetermined specificsecondary electron emissivity, isolated minute particles of a materialhaving a specific secondary electron emissivity diiferent from that ofthe electrode positioned on the electrode and forming a halfondaryelectrons emitted from the particles and I the electrode under theimpact of the deflected focused beam, said beam producing means, saidelectrode means and said metallic electrode being positioned within saidenvelope.

4. An electronic device comprising an envelope, an electron gun forproducing a beam of focused electrons positioned within the envelope, ametallic target electrode of predetermined specific secondary electronemissivity positioned within the envelope in register with the electrongun, a halftone picture formed of isolated particles of materialhaving aspecific secondary electron emissivity different from that of the targetelectrode positioned upon the target electrode, the areas of saidparticles corresponding to the density of the elemental areas of thehalf-tone picture, means within the envelope intermediate the gun andsaid target electrode for scanning said target electrode and thehalf-tone picture thereon by the focused beam of electrons, andelectrode means .within the envelope intermediate the target and thescanning means for collecting secondary electrons emitted from thehalf-tone picture and the target electrode under the impact of thescanning focused beam of electrons.

' MAX KNOLL.

BERNHARD BARTELS. OTTO SPENGLER.

